The present invention relates to the manufacture of diamond material and more particularly to chemical vapor deposition of diamond and diamond films.
Low pressure chemical vapor deposition (CVD) of diamond is an emerging technology with numerous potential applications. Serious efforts have been made to understand the mechanism for diamond formation under CVD conditions. A number of observations on the conditions favoring growth have been reported and mechanisms for the growth have been proposed. Prior known methods of diamond CVD employ a means of forming free radicals in a precursor gas, and it has been proposed that a key aspect of diamond CVD is the removal of non-diamond carbon by atomic hydrogen.
Free radicals are also believed to participate in the mechanism for diamond formation. By one proposed mechanism abstraction of a hydrogen creates a radical site on the growth surface. The growth is thought to proceed by addition of acetylene molecules. This proposed mechanism relies entirely on neutral species to initiate and propagate the growth.
An alternative proposed mechanism relies on a positive methyl ion to initiate the reaction. Growth of the diamond can then proceed with the addition of methyl radicals, as long as a positive charge is maintained on the substrate surface. This may provide an explanation for the observed effect of substrate potential on growth rate.
At least one researcher has reported evidence that negative ions can promote the formation of diamond. Pulsed plasma diamond crystallization experiments showed that diamond and graphite contents of the films varied with position of the substrate in the apparatus. Analysis of the chemical content of the plasma indicated that C.dbd.C molecules favor the formation of graphite, while C.sup.- ions were found where diamond formation was favored.
Japan Patent No. 63159292 illustrates the use of a high temperature mesh apparatus for exiting at high voltages the raw gas material in a large space. U.S. Pat. No. 3,961,103 shows a method and apparatus for depositing a thin film of material upon a base substrate including a glow discharge ion source.
The known processes for deposition suffer a number of disadvantages including the inability to create coating on selected areas of a substrate. During the use of electronic devices, heat is generated that must be dispersed. Diamond is both an electrical insulator and semiconductor and a heat conductor that would be useful in electronic devices if the diamond could be deposited in selected areas in appropriate patterns on the device. Moreover, in the coating of cutting tools, increased coating film thickness sometimes occurs at the corners or edges of the cutting tool. These thickened or bulb regions of the coating may be structurally weaker than the thinner regions of the coating. Moreover, the formation of the bulb may cause undesirable dimensional inaccuracies in the cutting tool and in the workpiece cut using the cutting tool.